Pulp screening machine

ABSTRACT

A pulp screening machine of the rotary type for either horizontal or vertical installation of either the open or pressure type in which the screen is made in sectors, joined together and one end place and a sector shaped screen supporting keeper plate and removed whereby the sectors of the screen plate can be removed axially of the machine without disturbing the screen housing in the line or the mounting of the impeller in the machine.

United States Patent Cowan 1541 PULP SCREENING MACHINE Ben Cowan, 5460Connaught Avenue, Montreal 29, Quebec, Canada 221 Filed: Jan. 19, 1970211 Appl. No.: 3,963

[72] Inventor:

[30] Foreign Application Priority Data Nov. 21, 1969 Canada ..068114[52] (1.8. CI ..209/273, 209/407, 210/232, 210/415 [51 Int. Cl ..B07bl/20 [58] Field of Search... ..209/407, 273, 270, 232, 415, 209/452,211, 370, 372; 210/403, 394, 210-215 [56] References Cited UNITED STATESPATENTS 3,508,651 4/1970 Hooper ..209/273X 51 May 23, 1972 3,057,476 10/l 962 Gilbert ..209/21 1 FOREIGN PATENTS OR APPLICATIONS 767,207 2/1952Germany ..209/407 Primary ExaminerFrank W. Lutter AssistantExaminerWilliam Cuchlinski, Jr. Attorney-Fetherstonhaugh and Co.

[57] ABSTRACT A pulp screening machine of the rotary type for eitherhorizontal or vertical installation of either the open or pressure typein which the screen is made in sectors, joined together and one endplace and a sector shaped screen supporting keeper plate and removedwhereby the sectors of the screen plate can be removed axially of themachine without disturbing the screen housing in the line or themounting of the impeller in the machine.

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3 IINVENT Ben COWA PATENT AGENTS PULP SCREENING MACHINE The inventionrelates to pulp screens of the rotary type, both open and pressure type,and particularly to means whereby the annular screen can be quickly andefliciently removed from its housing without disturbing the screenhousing in the line or the impeller and impeller mounting.

The invention is applicable to either open type gravity operated screensor to pressure type screens, either horizontal or vertically operated,but is of particular advantage in pressure type screens where thehousing is formed from a continuous cylindrical tube accessible onlyfrom the ends.

Paper pulp screens can be classified into two general designs, open(unpressurized screens), and pressure screens.

The open screens are normally fed with pulp under low pressures (6 tofeet of head) and discharge both accepted pulp and rejects atatmospheric pressure. The interior of the screen normally operates atatmospheric pressure. The unpressurized screen is generally moreselective and more efficient. It produces cleaner accepted pulp, and thequality and quantity of the rejected material can be closely controlledand adjusted.

The pressure screen operates at all times under a positive pressure inthe screen interior which may be of the order of 4 to psi. Both acceptsand rejects are discharged under pressure. The essential requirement isto avoid contact with air during the screening process and this avoidsthe generation of foam in the liquid medium. The rejects are difficultto control in quality, and there is a minimum quantity of rejects flownecessary to maintain operation. For this reason the pressurized screenis not as efficient in the removal of unacceptable material as the openscreen.

The open screen is generally built with the screen axis horizontal, anda fairly light frame with removable sections for screen plate screening.The pressure screen is generally built with the screen axis vertical,and a heavy body to withstand the internal pressure. The screen platesare less accessible and more difficult to change.

In summary the open screen is more efficient and flexible in operation,easier to maintain, and cheaper in construction than the pressurescreen. The pressure screen is a unit in a straight line flow system, issimpler to install, and does not generate foam.

The Multiple Screen of the present application is a design intended tocombine both applications, open or pressure, in a single unit. It uses acylindrical body for pressure resistance. The screen plate assembly is astandard three-section assembly used for all Cowan screens. Any standardCowan screen rotor can be installed in the screen which will allowoperation as an open screen with the K-X design of Cowan Rotor, or as apressure screen with the P-S or V type rotor. The assembly may also beset horizontal or vertical if required.

For maintenance and accessibility the front bearing is supported in ahollow beam submerged in the inlet chamber. This beam is open at bothends to atmosphere, so that no liquid can enter the bearing through thepacking gland. Any leakage of the packing gland is immediately apparentby the discharge at the open end of the support beam.

The end cover of the screen, at the inlet, can be removed for servicingand washing out the screen. To change screen plates, the top section ofkeeper plate only is removed, and the four small bolted covers on thehousing body of the screen which give access to the handholes. Thescreen plate sections are then unbolted and a 120 section of plateremoved through the opening caused by the removal of the top keeperplate. The other two sections of screen are then pushed up to the top,and removed in the same way. The screen frame is re-assembled in reverseorder.

If it is desired only to wash down the screen plate, the inside isaccessible through the feed opening without removing the keeper plate.The outside can be inspected and cleaned if necessary through thehandholes.

The object of the invention is to provide means whereby screen plates ina pulp screening machine can be withdrawn from a sealed housing withoutdismantling the housing or the impeller mounted within the housing.

A further object of the invention as used in pressure screening of pulp,is to provide means whereby the screen plates can be removed from theirhousing without taking the machine out of the line.

A still further object of the invention is to provide means wherebysectors of the annular screen plate can be removed individually from thescreen housing with a minimum of disturbance of the screen end plates.

These and other objects of the invention will be apparent from thefollowing detailed description and the accompanying drawings, in which:

FIG. 1 is a longitudinal vertical section of a horizontal pres sure typescreen showing typical elements of the present invention.

FIG. 2 is a view similar to FIG. 1 except that one external end 'plateand a portion of an adjacent internal end plate have been removed, andshowing a sector of screen plate partially withdrawn from the screenhousing.

FIG. 3 is a partial transverse section of one end of the screen housingshowing the inner bearing support beam.

FIG. 4 is a vertical section taken on the line 4-4 of FIG. 1.

FIG. 5 is a vertical section taken on the line 5-5 of FIG. 1.

FIG. 6 is a vertical section taken on the line 6-6 of FIG. 1.

FIG. 7 is an enlarged detail of a screen end support.

Referring to the drawings, the pulp screen 5 illustrated is typical of ahorizontal type pressure screen. However, the invention is not limitedin scope to horizontal pressure screens but could equally well beadapted to vertical pressure screens, or to horizontal and verticalgravity type screens.

The impeller 6 is of simple and well known type consisting of a shaft 7,blades 8 radiating outwards from the shaft, and baffle plates 9. Theimpeller 6 could be of the type having a conical core, and the blades 8could also be of the double wall type providing wash water passages,directing the wash water close to the inner surface of the screenplates.

The screen 5 is provided with a cylindrical housing 10 preferably of atype to withstand high internal pressure and be more or less retainedpermanently in the pulp stock line, the housing being dividedlongitudinally by the annular plate or partition 1 l to form a stockinlet chamber 12 and of a screening chamber 13.

A keeper plate 14 is bolted to the annular plate 11 by the bolts 15, andis made in two sectors, an upper sector 14a and a lower sector 14b. Theabutting edges 16 of the upper and lower sectors 14a and 14b aredisposed at an angle of approximately 20 above a horizontal plane normalto the longitudinal axis of the screen 5. The keeper plate 14 isprovided with an axial bore or opening 17 coincident with the axis ofthe impeller shaft 7, whereby stock from the stock inlet chamber 1 ispassed into the screening chamber 13.

A removable outer end wall plate or cover 18 seals the stock inletchamber 12 while a flanged pipe connection 19 at the upper end of thechamber 12 connects with a source of pulp, not shown, which may begravity feed or pressure feed to the interior of the housing.

An end plate 20 seals off the end of the screening chamber 13, oppositefrom the stock inlet chamber 12.

The annular screen 21 extends the full length of the screening chamber13 and is provided with end bearing rings 22 fitting over the supportrings 23 on the end plate 20 and over the support rings 24 on the keeperplate sectors 14a and 14b, thus allowing the screen to be manuallyrotated in the housing 10. The contacting surfaces between the rings 22and the rings 23 and 24 are slightly angled to reduce end play of thescreen 21 between the end plates 14 and 20, as shown in detail in FIG.1.

The annular screen 21 is made in three arcuate sectors or segments 21a,21b and 210 and are joined together at their abutting edges by pairs oflongitudinally disposed angle irons 25 by means of bolts or othersuitable fastening means.

Radially opposite each of the two upper abutting pairs of angle irons25, there is provided a pair of handholes 26 for ready access to thefastening means securing the screen sectors 21a, 21b or 210 together.These handholes 26 are closed and sealed by the cover plates 27.

The impeller shaft 7 is provided with an outer bearing 28 mounted on theouter facing surface of the end plate and is provided with a drivepulley 29. The shaft 7 is hollow and is provided with a wash water inletconnection 30. A series of apertures 31 through the wall of the hollowportion of the shaft 7 permits the wash water to be injected into thespace between the blades 8 of the impeller 6.

The end of the shaft 7, opposite from the wash water connectionterminates in a stub shaft 32 which is, in turn supported in the bearing33. The bearing 33 is mounted within a housing 34 which, in turn issupported in a hollow beam 35 disposed in a horizontal plane normal tothe axis of the impeller shaft 7. The end portions 36 of the beam 35 aresecured to the wall 37 of the stock inlet chamber 12 in line with the oenings 38 in the wall 37. A cover plate 39 seals the bearing 33 fromentry of fluid from the interior of the screen. A stuffing box 33aprevents fluid in the inlet chamber 12 from entry to the bearing 33.

Any leakage of fluid carrying the pulp which may penetrate into thebearing 33 will be carried along the interior of the hollow beam 34 andwill be discharged to atmosphere through the open ends 38.

The discharge of the screened pulp from the screening chamber 13 isthrough the discharge outlet 40, while heavy rejects are discharged fromthe interior of the screen plate 21 through the opening 41.

A clean out opening 42 is provided at the bottom of the inlet chamber12. This opening 42 may be closed by the removable plate 43 or by asuitable valve connection.

In order to remove the screen plate 21 from the machine for cleaning,repair or replacement, from the otherwise permanently sealed screeningchamber 13, as defined by the cylindrical housing 10, the end wall 18 isfirst removed. The upper sector 14a of the keeper plate 14 is thenremoved to expose the upper portions 2lb and 210 of the screen plate 21.

On removal of the cover plates 27 at the handholes 26, access isobtained to the fastening means at the angle irons 25 of the screensectors.

The screen sectors, when unsecured from each other, can be rotated ontheir support rings 23 and 24 to bring first one sector 21a andsuccessive sectors 21b and 21c opposite the enlarged sector openingcreated by removal of the upper sector 14a ofthe keeper plate 14.

As the sectors of the screen plate 21 are of three equal sectors of 120and the opening created by removal of the upper sector 14a of the keeperplate 14 is approximately 140, the individual sectors of the screenplate can be withdrawn with ease past the impeller and bearing 33 andits supporting beam 34. The upper edges 14c of the lower keeper plate1412 form a support for the screen plate sectors as they are beingwithdrawn.

It will therefore, be apparent that the screen plate 21 can be removedfrom its housing without having to remove the machine from the pulpline, or in any way interfering with the impeller and its mountingwithin the housing. It will also be apparent that a thorough cleaning ofthe interior of the housing, including the impeller can be accomplishedwhen the screen is removed as above described.

In addition, with the screen 21 removed as above described it is asimple matter to remove the complete impeller assembly, if desired,merely by disconnecting the end plate 20 from the housing 10, again,without taking the machine out of the pulp line.

The above procedure is reversed when either the impeller or the screenare to be reinserted into the housing.

Up to now the open type of screen has not been well adapted for use inpressure application because of the necessity for screen rem oval makesit difiicult to design a housing body which Wlll withstand high internalpressures. The present design, as above described, of an uninterruptedcylinder with easy screen removal, makes it feasible to use the samedesign of housing for both open and pressure screens.

The embodiment of the invention in which an exclusive property orprivilege is claimed are defined as follows:

ll. In a pulp screening apparatus, the combination of a sta tionaryhousing having a partition which separates the housing into a pulpscreening chamber and a pulp inlet chamber at one end of said screeningchamber, said inlet chamber having a removable cover opposite saidpartition, an impeller rotatably mounted in said housing, an annularscreen disposed in the screening chamber and surrounding said impeller,a keeper plate secured to said partition and provided with a centralopening which is coaxial with said impeller and communicates said inletchamber with the interior of the screen in the screening chamber, saidkeeper plate including a keeper plate sector which is removable fromsaid partition to provide an access passage additional to said centralopening, said annular screen consisting of a plurality of segmentsseparably connected together, and means mounting said screen for manualrotation in the screening chamber so that the individual screen segmentsmay be successively brought into alignment with said removable keeperplate sector, whereby upon removal of said cover and of said keeperplate sector and upon separation of the screen segments the segments maybe individually and successively removed from the screening chamberthrough said access passage and through the inlet chamber while leavingthe impeller in place.

2. Pulp screening apparatus as set forth in claim 1 which is furthercharacterized in that said annular screen consists of three segmentseach spanning an arc of said removable keeper plate sector having an arcspan greater than 120.

3. Pulp screening apparatus as set forth in claim 1 which is furthercharacterized in that the portion of said keeper plate other than saidremovable keeper plate sector is also remova ble from said partition.

4. Pulp screening apparatus as set forth in claim 1 in which saidimpeller includes a shaft, said shaft being supported in bearings, oneof said bearings being located within said pulp inlet chamber.

5. Pulp screening apparatus as set forth in claim 4 in which the supportfor the bearing within the pulp inlet chamber includes a hollow beamdisposed transversely within the inlet chamber and the ends of the beamare open to atmosphere externally of said inlet chamber.

6. Pulp screening apparatus as set forth in claim 5 in which saidbearing within the inlet chamber includes a stuffing box about theimpeller shaft and leakage through said stuffing box is drained toatmosphere through said hollow beam.

7. Pulp screening apparatus as set forth in claim 1 wherein saidscreening chamber has an end wall axially opposite said partition andwherein said screen mounting means comprise a pair of rings provided onsaid end wall and on said keeper plate concentrically with saidimpeller, end portions of said annular screen being rotatably supportedby said rings.

8. Pulp screening apparatus as set forth in claim 7 wherein saidmounting means also include axially projecting flanges provided at theends of said screen, said flanges being rotatably seated on said rings.

1. In a pulp screening apparatus, the combination of a stationaryhousing having a partition which separates the housing into a pulpscreening chamber and a pulp inlet chamber at one end of said screeningchamber, said inlet chamber having a removable cover opposite saidpartition, an impeller rotatably mounted in said housing, an annularscreen disposed in the screening chamber and surrounding said impeller,a keeper plate secured to said partition and provided with a centralopening which is coaxial with said impeller and communicates said inletchamber with the interior of the screen in the screening chamber, saidkeeper plate including a keeper plate sector which is removable fromsaid partition to provide an access passage additional to said centralopening, said annular screen consisting of a plurality of segmentsseparably connected together, and means mounting said screen for manualrotation in the screening chamber so that the individual screen segmentsmay be successively brought into alignment with said removable keeperplate sector, whereby upon removal of said cover and of said keeperplate sector and upon separation of the screen segments the segments maybe individually and successively removed from the screening chamberthrough said access passage and through the inlet chamber while leavingthe impeller in place.
 2. Pulp screening apparatus as set forth in claim1 which is further characterized in that said annular screen consists ofthree segments each spanning an arc of 120*, said removable keeper platesector having an arc span greater than 120*.
 3. Pulp screening apparatusas set forth in claim 1 which is further characterized in that theportion of said keeper plate other than said removable keeper platesector is also removable from said partition.
 4. Pulp screeningapparatus as set forth in claim 1 in which said impeller includes ashaft, said shaft being supported in bearings, one of said bearingsbeing located within said pulp inlet chamber.
 5. Pulp screeningapparatus as set forth in claim 4 in which the support for the bearingwithin the pulp inlet chamber includes a hollow beam disposedtransversely within the inlet chamber and the ends of The beam are opento atmosphere externally of said inlet chamber.
 6. Pulp screeningapparatus as set forth in claim 5 in which said bearing within the inletchamber includes a stuffing box about the impeller shaft and leakagethrough said stuffing box is drained to atmosphere through said hollowbeam.
 7. Pulp screening apparatus as set forth in claim 1 wherein saidscreening chamber has an end wall axially opposite said partition andwherein said screen mounting means comprise a pair of rings provided onsaid end wall and on said keeper plate concentrically with saidimpeller, end portions of said annular screen being rotatably supportedby said rings.
 8. Pulp screening apparatus as set forth in claim 7wherein said mounting means also include axially projecting flangesprovided at the ends of said screen, said flanges being rotatably seatedon said rings.